io86 Appendix VI. polygon, and join lines to corners. Commencing at any point on A draw the polygonal lines shewn in space diagram parallel to the radials in vector figure and in order, and letter as shewn. These lines are known as the links, and are lettered according to Bow's method. O c^ and 0 5X are the first and last links respectively, and at their intersection x is placed the resultant force line R, parallel to 05. The proof is very simple. Imagine the space polygon to be a framed structure or endless string held taut by the original forces. Every corner of this string has three forces, as for example Oji i1O Ool: and these have the force diagram O o i^. It follows that the whole of the vector figure is the force diagram for the framed structure, and if R'S direction be reversed all the forces are in balance. Two particular cases occur: (i) When the vector figure only is closed, o falling on 5, the resultant is a couple whose forces are each equal to O o or O 5, and whose area will be found from the space diagram; (2) when both polygons close, the resultant is zero, the forces being already balanced.